The use of gate arrays and standard cells has become well known as an effective and efficient method for rapidly developing new semiconductor products substantial complexity. Such standard cells are typically used in cell-based arrays, and have wide application within the industry. A widely-accepted design for a gate array architecture that provides standard cell type densities is based on the design described in U.S. Pat. No. 5,289,021, commonly assigned to the assignee of the present invention and incorporated herein by reference.
However, despite the many advantages offered by cell based arrays, prior art designs cells have suffered from some limitations which have become more apparent as line widths have been reduced and complexity has increased. In particular, the typical prior art standard cell has been limited to a relatively low ratio between compute and drive cells. In particular, prior art designs have limited the ratio between compute and drive cells to no more than three- or four-to-one. Moreover, manufacturing limitations have served to impose a fixed, three-to-one limitation on most if not all prior art designs. Although the three-to-one ratio has enabled efficient construction of a great many circuits, and is particularly well suited to many high performance designs, there remain other applications--for example, low power applications--which could benefit from a ratio of compute to drive cells other than (and typically greater than) three-to-one.
As a result, there has been a need to develop a cell based array design which permits the implementation of larger, and in some instances unlimited, ratios of compute to drive cells.